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more on "porosity" value


Tom Meuzelaar
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[admin notice: the below is from the former GWB users group email distribution list. This message was originally posted 5/19/2006]

 

Posted by: T.C. Onstott

 

Hello all,

 

In the process of trying to couple microbial redox reactions to

weathering reactions, I'm encountering three problems with GWB 6 that I

hope are easily resolved. They are as follows;

 

1) porosity - (see attached IRBAcetate2.txt file) - the output file

seems to ignore my inputed porosity value. GWB does seem to be

calculating porosity, but I cannot figure out how it is doing it nor

how it relates to my input porosity.

 

2) permeability - (see attached IRBSiliclastic.txt) - GWB6 doesn't seem

to recognize the permeability command at all -

 

3) mineral equilibration and charge balance - - (see

attached IRBSiliclastic.txt) - this is more serious - in this

code I'm equilibrating minerals with water, but in order to

obtain convergence I see to have to reduce the Na+ to ~1 mM values and then

the solution output is grossly out of charge balance - yet it

converged. how could this happen?

 

any help would be greatly appreciated as always.

 

thanks,

 

tco

 

 

Posted by: Craig Bethke

 

Hi TC,

 

Porosity is a derived value in React, not a prescribed value. To have the program calculate porosity from the volumes of fluid and minerals, type "porosity on", or simply "porosity". The command "porosity off" deselects the option. Extraneous arguments are ignored, so typing "porosity = 20%" is the same as just typing "porosity".

 

React does not consider Darcy flow, so there is no provision in the program for evaluating a permeability correlation, nor is there a "permeability" command.

 

You can see all of the commands recognized by React, along with their arguments and options and a description of their functions, in the "React Commands" chapter of the "GWB Reference Manual".

 

I'm guessing the reason you say the run you attach is "grossly out of charge balance" is because the concentrations of Na+ and Cl- don't match. In fact, the fluid in your model is dominantly a CaCl2 solution, so the Cl- is charge balanced by Ca++, not Na+.

 

Hope this helps,

Craig

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